It means that they have something good, and they can contain Napoli because their recent match was not good after having lead they lost by 2 - 3, In my view they are not taking seriously this Europa League and want to have better record in local league so just because of this they are not doing tough like they are doing in their local league.
Yes, this is a big chance for Legia if Napoli, with its Serie A lead in mind, prioritizes Europa League games much lower than Serie A games. In the end, the victory in the Europa League is very illusory, and leading the championship and not being distracted by anything, they can almost guaranteed to get into the Champions League next year, where there is many times more money, and if they are lucky, then become the champion of Italy.